The present invention is directed to a tension member protected against corrosion, mainly a tendon for prestressing concrete with post-tensioning. The tension member is formed of at least one tension element, such as a steel rod, wire or strand, located within a tubular envelope with anchoring devices arranged at the ends of the tension member. The tension member extends between anchor regions at the anchoring devices, with a free region extending between the anchor regions. In the free region, the tubular envelope is formed of a sheathing tube and is tightly secured to the anchoring devices in the anchor region. Open spaces are provided between the individual tension elements within the tubular envelope and at least in the region directly adjoining the anchoring devices the open spaces are filled with a plastically deformable corrosion-protection mass. Further, the invention is directed to a method of installing the tension member in a concrete structural member.
In structural design, particularly of bridge structures formed of prestressed concrete, prestressing with pretensioning and with post-tensioning is known. Prestressing with pretensioning is performed mainly as prestressing with subsequent pretensioning where the tendons or tension members remain free to move until the concrete sets and are subsequently bonded to the structure by injecting grout. In prestressing with post-tensioning, the tension members are generally located outside of the concrete structure, though they are supported relative to the structure, they can be inspected at any time, and,, if necessary, retensioned or replaced.
Tension members used as tendons for prestressed concrete with post-tensioning, or as diagonal cables for stayed cable bridges or for the rehabilitation of structural members and other structural tasks, require permanent corrosion protection made up of two independent corrosion protected systems with each system being completely effective by itself. A known tendon of this type, (Dyckerhoff & Widmann Publication "DYWIDAGL-Report", No. 11, 1982, page 7) is formed of a prestressed tendon surrounded by a polyethylene sheathing tube across the free region of the tendon. The annular space between the tendon and the sheathing tube is closed off at the ends of the tendon by seals and the annular space can be injected with a hardenable material, such as cement mortar. Such a hardening material forms the first corrosion protection system across the free region of the tendon, the second corrosion protection system is the sheathing tube itself. In the anchor regions, the sheathing tube is joined with a connecting tube and the connecting tube is joined to the anchoring plate of the anchoring device. To maintain the tendon so that it can be stressed, prestressed or replaced, the corrosion resistance in the anchor region is provided by a plastically deformable corrosion-protection mass, such as grease, filled under pressure into the annular space between the tendon and the connecting tube. Accordingly, in the anchor region, the first corrosion protection system is the corrosion protection mass and the second system is formed by the connecting tube joined to the anchoring plate.
With such an arrangement, doubtless there is the advantage that the use of a comparatively expensive corrosion protection mass can be limited to the anchor region, while the less expensive cement mortar is utilized for the free region of the tendon which represents a considerably larger volume. There is the disadvantage, however, that the cement mortar must be injected prior to the installation of the tendon, since the annular space in the free region of the tendon is not accessible after installation because an anchor tube is fixed to the anchoring plate. While this arrangement is acceptable in the case of individual tendons formed of a single tension rod, however, with bundled tendons, it is not acceptable, since the tendons could not be handled due to the great weight involved.
Furthermore, segmented fabrication of structures, such as the fabrication of bridge structures in the so-called time-shifting or incremental launching method often necessitates the provision of an additional tendon for a subsequent section to a tendon already anchored to the section, and the connection of such tendons, so that the entire tendon can be tensioned from the opposite ends.
For tendons with subsequent pretensioning so-called coupling points are known for joining the tendons. Thus, an anchoring and coupling device of one bundled tendon comprises one anchoring member which, in addition to conical bores for prestressed anchoring of the incoming tension members by means of wedges also has additional conical bores oriented in the opposite direction for anchoring the outgoing tension members (DE-PS No. 32 24 702). Such bores are arranged uniformly across the surface of the anchoring member. In this anchoring member, cylindrical bores follow the conical bores for anchoring the outgoing tensioning members and such bores are filled with a permanently plastic lubricating corrosion protection mass, whereby the tension elements are freely extended across these comparatively short. axial distances. By injecting the such as cement grout, a certain spring action of the tendon is utilized because of the short bond-free distance of the outgoing tension member, and the danger of crack formation in the coupling joint is reduced.